Waste heat is often created as a byproduct of industrial processes where flowing streams of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes utilize heat exchanger devices to capture and recycle waste heat back into the process via other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.
Therefore, waste heat may be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles or other power cycles. Rankine and similar thermodynamic cycles are typically steam-based processes that recover and utilize waste heat to generate steam for driving a turbine, turbo, or other expander connected to an electric generator, a pump, or other device.
An organic Rankine cycle utilizes a lower boiling-point working fluid, instead of water, during a traditional Rankine cycle. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbons, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa). More recently, in view of issues such as thermal instability, toxicity, flammability, and production cost of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate non-hydrocarbon working fluids, such as carbon dioxide.
In addition to the use of non-hydrocarbon fluids as working fluids in Rankine cycles, non-hydrocarbon fluids have also been used as a refrigerant in cooling circuits to cool machinery and electronics. For example, carbon dioxide has been used as a refrigerant in a multitude of processes and systems based on its low cost, abundance in the environment, and harmlessness to the biosphere. Moreover, carbon dioxide is an inert product, compatible with common materials encountered in a cooling circuit.
Therefore, there is a need for a heat engine system and method capable of transforming energy, whereby the non-hydrocarbon working fluid utilized in the heat engine system and method for transforming energy is also utilized as a refrigerant in a cooling circuit integrated within the heat engine system.